Regeneration of doctor solution



Jan. 2, 1945. H. H. WALKER Erm.

REGENERATION OF DOCTOR SOLUTION Filed Jan. 26, 1942 Patented Jan. 2, 1945 I 2,366,580 fnEGENERATrON or DOCTOR SOLUTION Harry`H. Walker and John P..Mos'tyn,Lockport, "Ill., 'assignors lto The 'I exas Company, New

York,-N. vY., a corporation of Delaware Application,January..2.6, 1942, Serial No. 428,218

' 'Thisinvention relates to :an improved process "of "svveetening hydrocarbon oils. More particularly the invention relates toa process of regenerating 'a spent-doctor solution..

For sweetening sour hydrocarbon oils such as naphtha, kerosene orgasoline, the process most Widelyl used is the-'so-called doctor process. In this process thesour oil-is contacted with 'an alkaline Asolution of ran alkali `metal plumbite, usually a vsolution 'prepared `by dissolving litharge in an Aaqueous solution of vcaustic soda. The process lalso usually involves treating the oil with free sulfur, which may be Iaddedibeioreor after fthe 'faddition of `doctor solution. The over-all result 4of vtreating a sour -oil in the 'above manner lis 'to l'convert the mercaptans, which limpart an unpleasantodor lto the oil, '.tooil-soluble, odorless "disuldea In accomplishing 'this'result the lead inthe sodium plumbite is converted tO insoluble lead sulfide which is settled out of the oil With the used doctor solution. Thus, while it is genferally recognized that 4side reactions take place concurrently, the mainreactions occurring inthe vdoctor treatment are considered to' be as follows:

(l) ZNaOH -i- PbO NazPbOz H2O Caustic Litharge Sodium 'Water l plumbite v(2) ZRSH 7|- NazPbOz (RS)2Pb -I- ZNaOH Mercaptan kSodium Lead Caustic gplumbite .mercaptide 3) (RsnPb 's l= .fR-ss-R Pbs Lead l.Sulfur Disulde Lead mercaptide sulfide IInthe'above equationsthe letter R represents the hydrocarbon :radical of .a :mercaptan A.present in Ithe sour oil.

In doctortreating itis customaryvto use an lfexcess of doctor zsolutionand, after the'reaction, thisfsolution is-removed `from .the treated voil by ,"settling, a plurality of lsettling tanks being used. Depending upon the tank system from which the used-doctor solution is removed, it is more or llessspent;z i. e.;sodium plumbitecontained therein thas v,beenfconverted .to4 lead sulfide. Thus a relatively completely spent doctorsolution ywill be rhighiin caustic soda content and willfcontain a large.l proportion ofr the-lead in the form of lead I4fsulde. Thespent doctor solution removed from 'fthe settling tanks 'also -.contains aproportion of the hydrocarbon toil Which will lvary in -amount f ependirlg upon the temperature maintained and other factors involved inthe treatment.

:Sincethe llitharge V.employed represents an important .item of expense the doctor. treatment, zit has been necessary toregenerate the spent docgas, in each stage.

.tor solutionin order't'omake tneiprocess'commercially feasible. This has been done by rst treating the solution so as to remove the major portion of the oil vcontained therein. Wherea large amount of the oil is in the solution the oil is usually present in emulsied form. This rst separation has'beenaccomplished by subjecting the solution to agitation and mild heating, and then settling to cause the solution vto separate into an oil phase and an aqueous phase. The aqueous phase-drawn ol after this 'settling will contain some hydrocarbon oil.

After the `separation :of :the .major portion of the hydrocarbon. oil, fthedoctor solution `has been regenerated by flowingit through anxopen tank in which it is heated .to an elevated temperature 'of the order of 195 :F.fand passing an oxygencontaining gas,"such as air, throughA the solution to oxidize leadsuldeto lead oxide, which reacts vWith thecaustic in the solutiony to form sodium plumbite. `Although'this procedure results in-a lregenerated Vdoctor solution, 4thecontrol is inexact, difficulties `due'to excessivefoaming are present, and the hydrocarbon oil is not recovered.

Itis a principal object vof the present invention to provide an improved process of regenerating spent doctor solution whereby substantially complete regeneration of the'solution may be assured, diiculties 'due'tofoaming maybe avoided, and Waste may be reduced.

'Otherobjects 'of theinvention in part will be obvious and in part'willappear hereinafter.

*In Vaccordance with'the presentinvention the regeneration of spent doctor solution is accomplished ina plurality of vstages inwhich the :temperatureis progressively increased, thesolution being subjected to the 'action voi" an oxidizing agent, preferably air or other oxygen-containing The temperature in each stage is adjusted so -as to accomplish maximum yregeneration While at the same time avoiding difT vilculties dueto foaming; The rate of aeration is also controlled in accordance With thesel objectives. Evolved vapors are rremoved during the regeneration and the hydrocarbons contained therein may be krecovered by condensing the vapors.

As. a`feature of the invention-it has been found that thelast stage of regeneration,-Which is conducted at `the maximum temperature required,

.normally from to 195 F.,'r nay be carried out effectively in ajclosed vessel from which evolved vapors are conducted through a conduit to a icondensation system. Thus, the hydrocarbons `in lthe vapors are'condensed andl recovered -vtogether with any entrained caustic that may be present. It has been found that the condensation and recovery of the vapors can be carried out efliciently by contacting the vapors with cool water; e. g. water at room temperature or in any event at a temperature .below the boiling point of the hydrocarbons. This may be accomplished by spraying water into the vapors, or by passing the vapors into the lower portion of a vessel containing baflles, Raschig rings or other means for causing intimate Contact of liquid and prior to a regeneration stage by an elongated conduit or chamber into which the vapors pass and wherein they are contacted with a water spray. The condensed hydrocarbons in the vapors are thereby returned into the system and they are recovered simply and eiciently.

By proceeding in the manner described, the regeneration of the doctor solution is accomplished eciently and the hydrocarbon loss is reduced. The process permits the use of relatively small equipment without difficulties due to foaming, for at the times when the solution contains a relatively large proportion of hydrocarbon oil the temperature is controlled to permit partial regeneration with lessened foam formation. Since the temperatures are gradually increased, in the early stages of regeneration hydrocarbon losses are small even where the vapors are not recovered, and in the final stage vigorous conditions may be maintained to complete regeneration and recover vaporized hydrocarbons.

In ycarrying out the process, it has been found to be advantageous to employ an aerating gas such as air itself in such marmer as to aid in causing the flow of the solution through the system. Thus, a portion of the air may be introduced between denite regeneration zones in the direction of ow of the solution. In this way the aeration is continued during ilow and the iiow of the solution is facilitated.

In order that the invention may be understood more fully reference should be had to the `accompanying drawing in which is shown a flow diagram illustrating one way in which the process may be carried out.

Referring to the drawing, the sour oil treated may be gasoline, naphtha, kerosene, etc., but theI operation will be described in Iconnection with the treatment of sour gasoline. The sour gasoline enters the system through line 2 at a rate of about 100 barrels per hour. From line 2 the gasoline passes into a line 4 wherein regenerateddoctor solution is flowing as will be described later. The doctor solution is preferably adjusted so as to contain about '7 pounds of lead oxide and 30 pounds of sodium hydroxide per barrel of solution, and the solution is mixed with the sour gasoline in an amount corresponding to about to barrels of solution for each 100 barrels of gasoline. 'Ihe mixed liquids then pass into a mixer 6 and then through line 8 into a conventional treating system diagrammatically illustrated at lmoved through line I6 and is introduced into the sour ycharge entering the system.

The doctor solution is pumped by means of pump I'I through lines I8 and I9 to a settler 20. At this point, in normal operation, the temperyature of the solution will be about to 90 F. r1"he settler 20 is preferably of large size and permits the separation of additional hydrocarbon oil which is removed through line 22 and is pref- Y Y erably subjected todistillation to remove tarry materials and produce a .clean oil. From this settler the doctor solution is pumped through line 24 by means of pump 25 and through line 26 to a heater 21 where the temperature may be raised to about F.

During the iiow of the solution from the settler 20 to the heater, air is preferably injected into the solution through line 28, the rate of air injection, for example, being of the order of 50 cubic feet' per minute. Thus, as the solution ows from the heater 21 through line 30 and into the make-up tank and settler 32, the regeneration of the solution may be initiated. The caustic soda that may be required for bringing the solution up to the desired caustic content may be introduced into this tank. Additional settling is accomplished here also and the oil separated may be removed through line 34 and the desirable fractions recovered by distillation. The doctor solution with reduced oil content is then passed through line 36 leading to a. vessel 38 in which the iirst substantial amount of regeneration is accomplished. The ilow of the solution through line 36 is aided and a part of the air required for regeneration is furnished by injecting air into line 36 through line 40. In this case the air may 'be injected at the rate of about 50 cubic feet per minute.

Vessel 38 is provided with a heating means such as a steam coil 42 and a means for injecting air such as spider 44. In this vessel the temperature of the solution may be raised to about F. and air may be injected at the rate of about 'I0 cubic feet per minute. Under these conditions partial regeneration is accomplished Without excessive foaming, and a small proportion of the low boiling hydrocarbons contained in the solution are vaporized and passed through vent pipe 46. These hydrocarbons may be recovered by condensation but in view of the relatively low temperature maintained, the recovery of the hydrocarbons is not essential for eicient operation of the process.

The partially regenerated doctor solution is removed through line 48 and then passes through line 49 or line 50 into one of two vessels 5I and 52 which are used alternatively and function as second stage regenerators. Air may be injected into the solution flowing in line 48, for example, at a rate of about fty cubic feet per minute by means of line 53. The second stage regenerators are provided with steam coils 54 and 55 and means 56 and 51 for injecting air. In these vessels the temperature of the solution may be raised to about F. and air may be injected at a rate of about 145 cubic feet per minute. The vapors formed are removed from the vessels throughA vent-pipes *5 8 aand "59, andfmafy'be recovered, @but khere also, since V`Vmajor evaporation of hydrocarbons is avoided due to the temperature maintained, the rprocess maybe :operated Lellivciently-without such recovery. 'The'solutionfleav at Aa rate of about `185 Ycubic. feet `per minute.

Under these conditions theregeneration of the doctor'solutionris substantially ecompleted. `The 'doctor solution which'is f-intr'oduceddnto regen- -erator 65,'due'dto the precedingsettlingand,heat- -ing steps, Awill normally contain 4 to L Beperxcent `hydrocarbon-oil. IIn-this -lregenerator vapors are 'formed which containvaluable-hydrocarbons-and perhaps -a small amountof-'entrainedcaustic. n Tol recover thefvaporizedhydrocarbons, regenerator'fi is closed to the atmosphere -butis-provided'wit'h an-exitpipe 68 leading to an elongatedhorizontal pipe `or chamber 59. There is ,s

, disposed in the pipe 6,9 a means 10 for introducing a spray of cool Water into the vapors. As shown, the pipe 69 leads to the settler 20 previously described, and the condensed hydrocarbons, together With the water introduced in the spray, pass into the settler where the hydrocarbons are separated along with the oil present in the incoming doctor solution, and are removed for treatment and recovery through line 22. The pipe 69 is provided with a vent 'H whereby the air and non-'condensible vapors may escape from the system. It Will be notedvthat by disposing the vent at this point, the flow of air assists in the movement of the condensed hydrocarbons and water to settler 20.

The substantially completely regenerated solution is removed from the bottom of regenerator 65 and passes through line 'l2 leading to a final settler 14. During its passage air is injected into line 12 through line 'i6 at a rate of, for example, 50 cubic feet per minute. This air serves to aid in moving the solution through pipe 'l2 and also functions to insure maximum regeneration. In settler 14 a small amount of remaining lead sludge and oil forms a narrow layer on top of the main body of the solution. Some of the oil contained in the solution entering this settler is vaporized and is passed through vapo-r line 18 into settler 20 where it condenses and is removed with the other oil from this vessel. The substantially clear and regenerated doctor solution is removed from settler 14 through line 80 and is cooled by means of cooler 82 to a temperature of about 80 to 90 F. and passes into line 84 leading to pump 86. This pump then pumps the solution into line 4 and into contact with the sour charge as previously described.

In the process illustrated lead sulphide recovered from the settlers forming part of the treating system, and make-up lead oxide maybe introduced at various points. It has been found to be satisfactory to introduce these materials into either of the second stage regenerators. The lead sulphide recovered in the settlers is the more easily precipitated product, and this product and the lead oxide are added in amounts and when necessary to maintain the proper concentration of lead oxide in the finished solution.

It will be understood that the specific condi tions of operation described in connection with l'the #fprocess shown in the 'drawing are V)merely illustrative oi thefinvention and that the invenftionfisnot. limitedto operating inljust this way.

lorexample,i there Vm-ayi be more-or fewerstages fof* regeneration v`and thetemperature `maintained in I the :stagesamay be ,varied` depending upon the jparticularequipment employed, the oil content r*of the -spent doctor solution, and the `foaming 5tendencies ofA the mixture. -As'pointed out above Ait-is general-ly=regardedwas preferable to lmainytain a temperaturefin each stage approaching the maximum Athat.- can 1 bemaintained in' the equipment-employed and .yetfiavoid excessive. foaming.

VIn general `itmay be stated that theregeneration 'is-accomplished ina plurality of stages inwhich Athe temperature is progressively-fincreased from vabouti-50" to Yabout 20 F.;theparticularftemperature-maintained in each-stage being determined as Ydescribed above.

, As previously indicated, 'fthe particular- -method elf-treating the sour oil-with the doctor solution tforms-no partofl the-*present invention, and-the doctor J-solution vmay -be -contacted f with vthe .sour

oil in any desired proportion. :For/example, it

Ihas-I beenproposedy to -contactfsour gasoline with tor solution containing hydrocarbon oil wherein an oxygen-containing gas is passed through the solution at regenerating temperatures, the improvement which comprises effecting substantial regeneration of the solution by the action of the oxygen-containing gas in each of a plurality of stages in which progressively higher regeneration temperatures of at least 150 F. are maintained, the amount of oxygen-containing gas employed in each stage being sucient to accomplish substantial regeneration of the solution in that stage, and the last stage being carried out in a closed reaction zone from which vapors including hydrocarbons are removed and recovered by condensation.

2. The process of regenerating spent doctor` solution and recovering hydrocarbons therefrom which comprises subjecting the doctor solution to a settling step to form a layer of hydrocarbon oil and a layer of aqueous doctor solution, recovering said hydrocarbon oil, eliecting substantial regeneration of the aqueous doctor solution by the action of an oxygen-containing gas in each of a plurality of regeneration stages maintained at progressively increased regenerating temperatures of at least 150 F., the amount of oxygencontaining gas employed in each stage being sufficient to accomplish substantial regeneration of the solution in that stage, carrying out a stage a closed reaction Zone, removing vapors including hydrocarbons from said zone, condensing hydrocarbons in said vapors by means of a water spray to form a mixed liquid comprising Water and hydrocarbon oil, and returning the mixed liquid to the settling step wherein hydrocarbon oil is settled and recovered from the spent doc` tor solution, whereby hydrocarbons in the doctor solution subjected to the action of the oXygencontaining gas are recovered.

3. The process of regenerating spent doctor solution and recovering hydrocarbons therefrom which comprises subjecting the doctor solution to a settling step to form a layer or hydrocarbon oil and a layer of aqueous doctor solution, recovering said hydrocarbon oil, flowing the aqueous doctor solution through a plurality of regeneration stages maintained at progressively increased temperatures Within the range from about 150 F. to about 200 F., passing air through the solution in each stage in an amount suicient to accomplish substantial regeneration of the solution in that stage, carrying out; a nal stage at a temperature from about 185 F. to about 200 F. in a closed reaction zone, removing vapors including hydrocarbons from said zone, condensing hydrocarbons in said vapors by means of a Water spray to form a mixed liquid comprising Water and hydrocarbon oil, and returning the mixed liquid to the settling step wherein hydrocarbon oil is settled and recovered from the spent doctonsolution, whereby hydrocarbons in the doctor solution entering the stage carried out in the closed reaction -zone are recovered.

4. The process of regenerating spent doctor solution containing hydrocarbon oil which comprises contacting the solution with an oxygencontaining gas in at least three stages maintained at progressively higher regeneration temperatures ranging from about to about 200 F., the amount of oxygen-containlng.gas contacted With the solution in each stage being sufficient to accomplish substantial regeneration of the solution in that stage, the temperature and amount of oxygen-containing gas employedI in each stage being adjusted such that said substantial amount of regeneration is accomplished While avoiding excessive foaming and vaporization of hydrocarbons, and the last stage being carried out at a temperature within the range of about to 200 F. and with the use of an amount of oxygen-containing gas effective to complete the regeneration of the doctor solution. 5. A process in accordance with claim 4 which comprises the additional step of injecting an oxygen-containing gas into the solution flowing between tWo stages to aid in regeneration and flow of the solution.

HARRY H. WALKER.

JOHN P. MOSTYN. 

